I actually found out what this is, so here's a little PSA for fellow users of iphone and Android: Sometimes, depending on what carrier you have (CDMS, GMS, etc) your carrier may have an SMS text limitation of 160 characters. If it exceeds that limit, the message will be broken up into smaller ones. Usually, this is fine. HOWEVER, sometimes different carriers that have these hard limits will not communicate well with carriers that don't have these limits. Example Verizon communicating with T-Mobile. Verizon is a CDMS with an SMS hard limit of 160, this is for SMS, not imessage. T-mobile tries to re-assemble broken up SMS messages into one long form text because it's a GMS carrier.
What can happen is long text messages are either not received, received out of order, or (this is common with iphones trying to communicate with Androids) messages will get REALLY mixed up and the receiver will get chunks of old messages mashed together with pieces of a new message. This is what has happened when you get weird messages you never typed. It can assemble any number of old messages with new ones, so you'll either get indecipherable frankenmessages, or you'll get messages mashed together that look a hell of a lot worse than what they are.
So everyone who said this was "shenanigans," no, actually, it isn't.
My situation thankfully resolved itself. After searching for answers all day, I found the apple discussion forums on which someone had asked the same question about the same problem. I also searched the T-Mobile site for answers. That's how I learned about the difference between CDMS and GMS carriers. The message my boyfriend received consisted of the last word and a half of what I MEANT to send him, and the first half of a text I had sent him back in June about the people in the street partying after the Hawks had won a game.
Now, he is still on T-mobile as a carrier, and I still use Verizon, however, he now has an iphone 6, and is able to use imessage, so this problem has not happened again.